Sure hacking may be one cause, but so could account sharing, account buying, a friend giving you an old account or even something as simple as a move of address during the lifetime of the account (especially if its an international move). There can be several causes of such things happening. Its just a statement of fact that the data on record suggests that the account was created by a different source than the one you have evidence for. I wouldn't say that's calling you a liar or a hacker. This shouldn’t be the end of your adventures, as we know the likelihood is that this account was given to you in good faith by a friend, so we really hope you continue to play on any existing accounts you own, or you create a new account to begin a brand new adventure. We are here to help and if you have any questions about accounts you did create, you can contact us any time. We hate to see players like yourself disappointed, which is why these rules are in place to protect you from investing time and sometimes money into an account you will likely lose later down the line to the original creator. We state in our ‘ Rules of RuneScape’ that “players should not accept an account that anybody else offers as they may be stolen” to try and prevent issues like this. We always look to return accounts to their rightful owners, and whilst I can see you have been on the account in the past, it’s clear you didn’t create it.
After getting a second opinion from a fellow mod to make sure I haven’t left any stone unturned, we can see that someone else is the creator of the account. Using the information you have provided (thank you!), I have been able to cross reference this with the evidence on our systems. Thank you for contacting Jagex Customer Support.